1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit, and, in particular, to such a linear motion rolling contact guide unit having an enhanced seal characteristic.
2. Description of the Prior Art
A linear motion guide unit is well known in the art, and it generally includes a rail, a slider and a plurality of rolling members interposed between the rail and the slider for providing a rolling contact between the rail and the slider. There are basically two types of such a linear motion guide unit, i.e., the infinite stroke type and the finite stroke type. Such a typical prior art linear motion guide unit is illustrated in FIG. 7. As shown, the illustrated linear motion guide unit includes a rail 1a extending straight over a desired length, a slider 3 slidably mounted on the rail 1a in a straddling manner, and a plurality of balls 2 as rolling members interposed between the rail 1a and the slider 3. Use may also be made of rollers as rolling members in place of balls 2.
In the structure shown in FIG. 7, the rail 1a is elongated in shape and has a generally square or rectangular cross section so that it has a pair of opposite side surfaces 4a, each of which is formed with an inner guide groove 5 extending in parallel with the longitudinal axis of the rail 1a. Thus, the structure shown in FIG. 7 provides a two guide channel type linear motion guide unit. Alternatively, as shown in FIG. 8, another inner guide groove may be formed in each of the opposite side surfaces, or at the top thereof, of the rail 1a, in which case a four guide channel type linear motion guide unit is provided.
As shown in FIG. 7, the rail 1a is provided with a plurality of mounting holes 26 through which bolts or the like may be inserted to have the rail 1a fixedly mounted on a desired object. On the other hand, the slider 3 typically has a U-shaped cross section, including a horizontal section and a pair of side sections depending from the opposite sides of the horizontal section, so that the slider 3 is slidably mounted on the rail 1a in a straddling manner. The slider 3 is typically provided with a pair of endless circulating paths, including a load path section, a return path section 11 and a pair of curved connecting path sections connecting the corresponding ends of the load and return path sections as well known in the art. An outer guide groove 1 is formed in a surface of each of the side sections of the slider 3 in an opposed relationship with a corresponding one of the inner guide grooves 5 of the rail to thereby define a load path section as a guide channel between the associated pair of inner and outer guide grooves.
A plurality of rolling members or balls 2 in the illustrated example are provided in each of the endless circulating paths so that the balls 2 in the load path sections provide a rolling contact between the rail 1a and the slider 3 and therefore the slider 3 may move relative to the rail 1a as long as the rail 1a extends.
When the slider 3 is detached from the rail 1a for some reason, such as maintenance or repair, mostly those balls 2 which are located in the load path sections fall off. If this happens, it would be extremely difficult to put all of the balls 2 back in position when the slider 3 is mounted on the rail 1a once again. Thus, in order to prevent the balls from falling off when the slider 3 is removed from the rail 1a, a ball retaining member 18 extending generally along the load path section is provided with its both ends fixedly attached to the slider 3 so as to prevent the balls from falling off when the slider 3 is detached from the rail 1a.
Such a ball retaining member 18 is integral with and thus moves with the slider 3 and thus it must be located not to scrub against the rail 1a when the slider 3 moves relative to the rail 1a. For this reason, a relief trench 6a is provided at the bottom of each of the inner guide grooves 5 extending in parallel with the longitudinal axis of the rail 1a to receive therein a portion of the ball retaining member 18 without contact. In the prior art, such a relief trench 6a is typically either square or rectangular in shape. Incidentally, in the structure shown in FIG. 8, the additional guide groove is not provided with a relief trench; however, as well known in the art, a plate-shaped projection is typically provided on the slider 3 to project therefrom toward the balls 2 to retain the balls 2 in position, though such a projection is not shown specifically.
Now, a typical prior art method for manufacturing the rail 1a will be described with reference to FIGS. 4 through 6.
(a) As shown in FIG. 4, a rail intermediate product 19 having a shape indicated by the two-dotted line is formed from an alloy steel material or the like by drawing. The rail intermediate member 19 includes a top surface 20, a side surface 21 and a bottom surface 24. The side surface 21 is formed with a guide groove portion 22 and a side recess portion 23.
(b) After drawing, a relief trench 6a for receiving therein a corresponding ball retaining member 18 is formed at the bottom of each of inner guide grooves 22 by milling as shown in FIG. 5.
(c) Then, a guide surface of the inner guide groove 22 is hardened by induction hardening.
(d) Then, after removing distortions due to heat treatment, selected portions of the rail intermediate product 19, including a top surface portion 20, a guide groove portion 22, a side surface portion 21 and a bottom surface portion 24, as indicated by the fat lines in FIG. 6, are ground to thereby finish the rail guide groove 5 and side surface 4a to a desired shape and accuracy, as shown by the solid line in FIG. 4.
Additional steps, such as a step for providing the mounting hole 26, are also carried out, but such additional steps are omitted since they do not form a part of the present invention. In FIG. 4, a contact relationship between the finished guide groove 5 and an associated ball 2 is illustrated. It is to be noted that a side recess 7a(23) remains unprocessed after drawing as indicated by the dotted line in FIG. 6.
In accordance with the prior art, the relief trench 6a is formed by milling irrespective of the length of the rail 1a to be manufactured. Thus, if the rail 1a is relatively long, there may be produced a larger deformation after heat treatment so that there arise fluctuations in the position of the relief trench 6a. Thus, after grinding, when the rail 1a and the slider 3 are assembled, there arises a case in which the ball retaining member 18 is in contact with the relief trench 6a of the rail 1a. In order to avoid such an inconvenience, the width of the relief trench 6a must be made significantly larger as compared with the size of the ball retaining member 18. It is disadvantageous to set the width of the relief trench 6a larger since the effective ball bearing portion of the guide groove 5 is reduced and the rigidity of the guide groove 5 is also reduced.
As shown in FIG. 7, the slider 3 is generally comprised of a center block 8 and a pair of front and rear end blocks 9 each fixedly attached to each end of the center block 8. In the structure shown in FIG. 7, since a pair of endless circulating paths including a load path section, a return path section 11 and a pair of curved connecting path sections connecting the corresponding ends of the load and return path sections is provided, the load and return path sections are defined in the center block 8 and the curved connecting path sections are defined in both of the front and rear end blocks 9. It is to be noted, however, that the guide unit shown in FIG. 7 may also be constructed to be of the finite stroke type in which no endless circulating paths are provided. The end blocks 9 are also typically formed with a lubricant distributing system, and a grease nipple 12 is also provided as inserted into the end block 9.
Each of the end blocks 9 is provided with an end seal 13 which projects forwardly or rearwardly and which has a lip 14 defined at its tip end to be in sliding contact with the top surface 15, side surface 4a and guide groove 5 of the rail 1a so as to prevent any undesired foreign matter from entering into a gap between the rail 1a and the slider 3. However, in the prior art structure, the end seal lip 14 is only disposed to be in the vicinity of the relief trench 6a and not in sliding contact therewith. Moreover, a bottom seal 16 is also mounted at the bottom surface of the center block 8 of the slider 3. The bottom seal 16 has a lip 17 defined at its tip end, but the lip 17 is only disposed to be in the vicinity of the side recess 7a and not in sliding contact therewith. In this manner, since the seal lips 14 and 17 are not provided to be in sliding contact with corresponding surface portions of the rail 1a, there are defined open gaps which could allow any undesired foreign matter to enter into the gap between the rail 1a and the slider 3, which is extremely disadvantageous. The reason why the end seal lip 14 cannot be set in sliding contact with the corresponding relief trench 6a is because the relief trench 6a provides a rough surface. This is so because the relief trench 6a has been formed by milling. In addition, because of errors in positional relationship between the guide groove 5 and the relief trench 6a, a sliding contact between the end seal lip. 14 and the surface of the relief trench 6a would fluctuate significantly and thus the seal end lip 14 may be temporarily separated away from the surface of the relief trench 6a during operation. In addition, the seal lip 17 of the bottom seal 16 cannot be brought into sliding contact with the side recess 7a since the side recess 7a is an unprocessed and thus an extremely rough surface.
In addition, since the processing of the relief trench 6a and the processing of the guide groove 5 are carried out separately and before and after heat treatment in the prior art process, an absolute shift in position between the relief trench 6a and the guide groove 5 tends to be amplified, which can also be a cause of a sliding contact between the ball retaining member 18 and the relief trench 6a. Furthermore, since the side recess 7a(23) (FIG. 4) of the rail 1a remains unprocessed after drawing, a bottom surface seal 16 of the slider 3 cannot be brought into sliding contact with the side recess 7a(23), and, thus, the sealing characteristic between the rail 1a and the slider 3 remains incomplete in this respect also.